In recent years, a global navigation satellite system (GNSS) is used to specify a three-dimensional position on the earth. While this GNSS involves point positioning with low accuracy and relative positioning with high accuracy, recently, a scheme with high accuracy has been proposed also in point positioning.
While this positioning scheme uses two radio waves for signal transportation used in the GNSS, that is, dual frequency to thereby measure a distance between a satellite and an observatory station, that is, a mobile station, with high accuracy, this positioning scheme has a drawback that a positioning apparatus using dual frequency becomes expensive. Therefore, a positioning method for enabling point positioning using a single frequency has been proposed. This positioning method is based on an RTK (Real Time Kinematic) positioning scheme and requires a reference station to be located in the vicinity of the mobile station (see, for example, WO 2011/054082 A1).
By the way, in the case of the RTK positioning scheme, when a distance between the reference station and the mobile station exceeds a few kilometers, a delay error due to the ionosphere and a delay error due to the troposphere between the reference station and the mobile station become large, making it impossible to obtain ambiguity. That is, it becomes impossible to perform positioning with an accuracy of centimeters. Typically, when the distance exceeds 5 kilometers, it is impossible to solve ambiguity with the RTK positioning scheme using single frequency. That is, the positioning scheme requiring determination of ambiguity, disadvantageously requires an expensive dual frequency GNSS receiver.